Bontrager Ant+ cadence/speed sensor review

Bontrager’s excellent Ant+ speed and cadence sensors can be quickly fitted to any bike to provide top-quality metrics…

Because try as you might, your cranks just don’t overlap your wheel?

When it comes to performance metrics, I’m a big fan of the Ant+ standard – it’s supported by a wide range of dedicated devices like the Garmin Edge series GPS, as well as Android phones like the Xperia Active. It’s the native comms protocol for heart rate monitors, speed/cadence sensors and the more expensive category of cycling power meters (SRM, Quark, Vector, PowerTap…)

Unfortunately, your typical Ant+ speed/cadence sensor just isn’t compatible with laid-back cycling. Devices like the highly recommended Garmin GSC-10 rely on the fact that you can stick a sensor on the chainstay of a diamond-frame bike and it can ‘see’ a spoke magnet (for wheel speed) and a crank magnet (for cadence) from the same location. Try that on a bike where the pedals are several feet from the nearest frame member overlapping a wheel!


Enter Bontrager’s Interchange range of Ant+ digital sensors, which includes two of particular note for recumbent riders: discrete speed (part #424633) and cadence (part #426479) sensors!

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1 minute: upright vs MetaBike power

Comparing power output on the MetaBike versus upright DF bike on a one minute max effort hill climb…

Following my recent PowerTap test of the RaptoBike Midracer / DF racer, I said I hadn’t bothered to record a maximal effort on both bikes because the figure would reflect a lot of inequalities:

  • how much have I been riding either type of bike?
  • are the tyres comparable?
  • how efficient are the particular drivetrains (is one chain dirty and the other clean?)
  • what’s going on with frame flex?
  • etc. etc.

However, more than one person in various forum discussions said I should record maximal uphill efforts on both platforms to provide some backdrop, despite the fact that it wouldn’t isolate a particular factor.

Edinburgh’s Observatory Rd: short but sweet…

So, against my better judgement 😉 I ran a head-to-head between the MetaBike I had out on trial (known to be one of the stiffer and better climbing recumbents) and my all-steel commuter bike. I chose the commuter because the all-up weights of both bikes come very close – possibly the DF is a little heavier in fact…
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Powertap: convert watts to calories burned

Calculating calories (kcal) consumption for given wattages using a cycling power meter, such as a PowerTap.

Calculating a hard baseline for energy expenditure

PowerTap. After the immediate thrill of “how many watts can I do?” (answer: disappointingly few!), I moved on to the next most obvious question: “how fast will my bike(s) go for a given wattage?

However, there’s another side to measuring power output which I hadn’t really considered until some time after I built up my PowerTap. You actually know how much energy you put into the road over the course of a ride (or part of a ride).


Turning watts into calories

If you know duration and average power you already have energy, it’s just not expressed in good old-fashioned calories. It turns out there’s a suprisingly simple formula to turn the wattage from a power meter into kcal though:

energy (kcal) = avg power (W) X duration (hours) X 3.6

As with so many surprisingly straightforward looking formulae, there are assumptions built into the constant.

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Milan velomobile hits the road

It’s been a while since I posted an update on the Milan that was put together in Edinburgh’s Laid-Back-Bikes over the summer months (see previous posts).

Back at the start of August update the Milan was complete barring electrical work. The bike was provided with twin B&M headlights (to be run from a battery) but otherwise needed to be drilled and extensively wired for switched indicators and a rear light.

Finally time came for the Milan to launch and be ridden home to the west coast (a respectable day’s ride).

Outside Laid-Back-Bikes in Marchmont

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Upright (Strava bike) weight analysis

A while back I published a post looking at the weight of my recumbent (the RaptoBike lowracer). Here’s a nice contrast – when I built my upright Strava bike I also weighed all the parts as I was putting it together.

Again (as I keep saying!) I think that weight as a commodity is vastly overrated. Still, I have to recognize that a lot of people disagree, and it is interesting to see where the differences between a recumbent and upright bike are.

Strava bike weight
Planet X Superlight Team Aluminium

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Aussie government funds scientists: find helmets great after all

After the authors’ previous paper was critically panned, is this really the last word on Australian bike helmet laws?

Dance of the academics continues amidst media glee

When everyone already wears a helmet, what’s really causing falling injury rates?

As the fallout from Australia’s failed bike sharing schemes continues, it seems we haven’t seen the last of government-funded research showing that helmet laws are great actually, thanks very much.

Long term bicycle related head injury trends for New South Wales, Australia following mandatory helmet legislation (Olivier, Walter and Grzebieta, 2012) has just made a splash on BikeRadar and various forums after being accepted by the journal Accident Analysis and Prevention.

The authors, Olivier, Walter and Grzebieta, previously published a paper in 2011 claiming to “end the debate about the effectiveness of cycle helmet legislation”, but which was severely criticised by fellow boffins:

The dataset is unsound. Lesser severity cyclist head injuries, mostly in falls, were compared with high severity pedestrian head injuries in road traffic accidents. In addition, the definition of head injury was broad, including low severity injuries such as scalp wounds and bruising. Despite this, the comparison of pedestrian and cyclist injury ratios does not show a noticeable, sustained improvement for cyclists after the legislation came into force. This adds to previous studies that claimed an effect from helmet legislation, yet upon re-evaluation of the data, a null result was concluded.

via Bicycle Helmet Research Foundation

It seems that Olivier et al are back for another shot, this time using the ratio of cyclist arm:head injuries without that pesky comparison with pedestrian injuries thrown into the mix. They’re also only considering hospital admissions, rather than any recorded injury (on which more later).
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RaptoBike Midracer review

Promising the same winning ride quality, flexibility and speed packaged around two full-size 700C wheels… not to forget the affordable pricing.

Can it live up to the hype?

Front wheel drive for big wheels in a fast, versatile and robust package

Way back in 2008 Arnold Ligtvoet’s RaptoBike lowracer caused a storm when it hit the streets (going on to win the Bentrider Bike of the Year Reader’s Choice amongst other plaudits).

It didn’t take long before word got out that Arnold was tackling a midracer as his next project, promising the same winning ride quality, flexibility and speed packaged around two full-size 700C wheels… not to forget the affordable pricing.

RaptoBike Midracer review

One way or another it took a couple of years to see the light of day, but courtesy of Edinburgh’s Laid-Back-Bikes the RaptoBike midracer is indeed here in the flesh!

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